Leather softening adhesive



Dec. 25, 1951 T. GELINAS LEATHER SOFTENING ADHESIVE Filed March 23, 1950 VISCOSITY CENTIPOIES NORMAL PROPYL ALCOHOL.

THE RELATIONSHIP BETWEEN VISCOSITY AND SOLVENT CONTENT FOR MIXTURES OF NATURAL LATEX AND VARIOUS SOLVENTS CONTAINING 40 PER CENT BY WEIGHT OF RUBBER SOLIDS PER CENT BY WEIGHT OF SOLVENT I l I I 2 SI-IEETSSHEET 1 "ISOPROPYL ALCOHOL ETHYL ALCOHOL lg ACETONE :METHYL ALCOHOL Dec. 25, 1951 Filed March 25, 1950 T. GELINAS 2,580,167

LEATHER SOF'TENING ADHESIVE 2 SHEETSSHEET 2 THE RELATIONSHIP BETWEEN VISCOSITY AND ISO- PROPYL ALCOHOL CONTENT FOR COMPOSITIONS OF BBTEX 8I8H ADHESIVE,,WATER AND ISO-PROPYL ALCOHOL FOR COMPOSITIONS OF VARIOUS TOTAL SOLIDS CONTENT 3| PER CENT TOTAL SOLIDS 27 PER CENT TOTAL SOLIDS 23 PER CENT TOTAL SOLIDS PER CENT BY WEIGHT OF PROPYL ALCOHOL I I l r I I Patented Dec. 25, 1951 tries I :ilna'rnan sorrsnme ADHESIVE .Thu ibe Gelinas Rochester, N. -H.,- assignor to Hubbard Shoe 'Gompany,=-Ircorporated,. Rochester,- N t H a corporation of New Hampshire nppiitationMmh 2a, 1950, Serial No.,151,399

This invention compris s-a new and improved adhesive containing l-Ievea latex and rropyl alcohol. One object of the invention is to p ovide an adhesive p rticularlyadapted for leat er d e folding operations and. which is characterized by a no nced cana irv for enetrat n i to the leather and softenin it. thereby reducing the tendency for the leath r to crack when fled. Another object is to provide an adh sive h ving a natural latex base characterized by high penetra ilitv for which property the viscos y has not been imnaired'nor the physical stability of the dispersion lessened.

In fabricating articl s made from leather it is often desirable tofinishthe leather ed es by folding them. This process is commo y u ed on the up er ed es of the Vam s of shoes to improve the appearance of the-shoe and to increase the resistance of the edge to tearing. Fo din the edge also increases its resistance to absorption of moisture by-extending the finished, relatively moisture-resistant outside surface of the leather around the edge of the article end bringing the edge of leather into aregion l ss likely to become wet. A convenient method of folding the edge ,is to apply an adhesive tothe inside orunfinishe'd surface of the leatherqalong the marginalregion, fold themarginal region lengthwise bringing together adhesive-covered surfaces, and'then apply pressure .to squeeze the adhesive covered surfaces together.

The pressure applied duringthis folding. operation sub ects'the finished outside surface. of the leather to a combination of bending andztem sional stresses. The tensional stresses .can be reduced :by skiving the edge tomakeitgthinner, but, this results in sharper :bending ,astresses. Frequently the folded edge :irorn the combination of thesestresses. Softenin the leather minimizes this tendency. :Softening .a'ggents have been heretofore applied to the 1 ther prior tothe application oftheeadhesive. A? equently they ,consistof aqueous solutionsof soaps ,or detergents, the water-..acting;; as the ;softening agent and the; soap or detergent act- ;ing toreduce surface tension and aid penetration.

Organic solvents which will penetrate the advantage of ren'dering th e'leather more or less permanently soft.

The incorporation of leather-softening agents into atex-base adhesives h s presented serious problems. "The adhesive must be penetrating in action. "It'is not suflicient merely to addsap,

detergents or other surface activating m terials since penetrability depends also on viscosity and that is an independ nt and limitin factor. Consequently the viscosity must'genera lybereduced. This for maximum penetrabiity may be done by diluting the latex, resulting in an 'adhedve which is less stable physical y and often too fluid to be app ied in filmsof 'o timum thickness. Satisfactoryadhesives may be sometimes produced by efiecting a compromise, sacrificing stability and viscosity for adequate penetrabi'ity. It has not been considered pr ctical to increase the penet ability of an ad esive by adding water-miscible organic sofvents because theirtendency' in general is to cause coagulation oi the latex. This is probably caused :loy the dehydrating effect of such solvents. The :expecte'd'result ofrsuchanaddition would also be areduction in viscosity.

' My invention provides. an adhesive which does inot have "the limitations of 'prior adhe ives, It 3113 highly penetrating action, and thatprop- -erty-has not been imparted to it by alowering -50f viscosity nor a lessening of stability. =penetrability-renders it softening in action when applied to leather.

Its

The invention is based upon the discovery that when propyl alcohol, either normal or-iso, is added to'natural latex the viscosityris increased, the stability is not impaired and "the resulting composition is high y rene- *tratingin: action. While the softening effect of .this adhesive is temporary, being dependent upon .the presence of water and.v propyl'alcohol,

can incorporate'in it softening agents of more permanent typewhich the penetrating action of the'adhesive will carrywell into the'leather.

Since. propyl alcohol is a dehydrating solvent it -has;somettendency to cause-latex to-coagu- :late. .I'attributeithe stability of my'improved adhesives to theunexpected effect-of theproyl aa-lcohol'in increasing 'itsviscosity. Propyl a1- into leatherwill also. generally softenit. This .is true of methyl alcohol, ethyl alcohol, acec'ohol may-therefore'be added insuch amounts :that the latex is diluted to the extent that vis- 'cosityiis no longer increased. I have found that 'I' can incorporate as much as 18 per centby weight of-propyl alcohol in a compositioncontaining 40 per centby weight of rubber-solids.

Preferably I produce my-imp'roved -adhesive-by adding mixtures of propyl alcohol and water to adhesives. The proportions depend on the desired concentrations of propyl alcohol and rubber solids in the adhesive and on the rubber solids content of the latex to be used. I use mixtures of propyl alcohol and water, rather than concentrated propyl alcohol, to avoid the coagulating effect of local concentrations of propyl alcohol on the latex during the addition. To minimize further this possible coagulating effect I add the propyl alcohol-water mixture slowly while stirring the latex gently.

To produce my improved adhesive, containing 40 per cent by weight rubber solids and 18 per cent by weight of propyl alcohol from latex having 60 per cent total solids I proceed as follows:

Example 1 First mix together 18 parts by weight of isopropyl alcohol and parts by weight of water. Then add this, slowly while stirring, to 67 parts by weight of Hevea latex having 60 per cent total rubber solids.

This composition is adequately stable and has a viscosity of 250 centipoises. The viscosity of 60 per cent latex is about 80 centipoisesand that of 40 per cent latex is about 20 centipoises.

Other satisfactory compositions having varying amounts of iso-propyl alcohol may be mixed by the same procedure. To prepare 100 parts of a composition having a propyl alcohol content of a: per cent and a solids content of y per cent from a latex having a solids content of a per cent, the proper proportions can be calculated from the following formulae:

a=100y/z b=m c=100l00y/z':1: where a=parts by weight of latex b=parts by. weight of propyl alcohol c=parts by Weight of water.

The characteristics of my novel adhesive will be better understood and appreciated by reference to the accompanying drawings in which:

Fig. 1 is a graph showing the relationship between viscosity, represented by the ordinate, and solvent content, represented by the abscissa, for mixtures of Hevea latex and various solvents and containing 40 per cent by weight of rubber solids,

Fig. 2 is a graph showing the relationship between viscosity, represented by the ordinate and iso-propyl alcohol content, represented by the abscissa, for compositions containing a commercial latex-base adhesive, water and iso-propyl alcohol and having various total solids content.

.The effect of iso-propyl alcohol on the viscosity of mixtures containing 40 per cent by weight of rubber solids is shown in Fig. 1. It will there be seen that iso-propyl alcohol has its most marked efiect on viscosity at concentrations greater than about nine per cent by weight, but my invention is not limited to such range.

The effect of various other water-miscible organic solvents on the viscosity of latex is strikingly different from propyl alcohol. These solvents include acetone, methyl alcohol and ethyl alcohol. The effect of these solvents on the viscosity of latex is shown also in Fig. 1. Ethyl alcohol had the greatest tendency to increase the voscosity, but at concentration of 18 per cent the viscosity was only increased by about 35 centipoise units, whereas iso-propyl alcohol increased it by about 230 centipoise units.

While all the above examples of my improved adhesive show mixtures comprising latex and iso-propyl alcohol it is a fact that normal propyl alcohol may also be used.

Example 2 A composition containing 13 per cent by weight of normal propyl alcohol and 40 per cent by weight of rubber solids was prepared as set forth above but with normal propyl alcohol substituted for iso-propyl alcohol. The viscosity was found to be 62 centipoises. This composition is represented on the graph of Fig. 1 by the point marked normal propyl alcohol. It will be seen that the result is consistent with the results observed for iso-propyl alcohol. Iso-propyl alcohol however has the advantage of lower cost.

The improved adhesive of my invention may be produced from commercial latex-base rather than from pure latex, and may include less than about ten per cent by weight of propyl alcohol, and

about 25 per cent by weight of total solids.

A typical latex-base adhesive is BB Tex 8181-1 sold by the B. B. Chemical Company, Cambridge, Massachusetts. This material contains about 36 per cent by weight of total solids (of which about per cent by weight is rubber solids) and has a viscosity of about 2800 centipoises. This material maybe diluted with a mixture of propyl alcohol and water to reduce the solids content to about 25 per cent by weight, thereby also reducing the viscosity. By using a propyl alcoholwater mixture I am able to maintain a higher viscosity and a greater physical stability than by using water alone as the diluent. Such compositions are prepared in the manner set forth above.

The proportion of water, propyl alcohol and latexbase adhesive are dependent upon the desired concentrations of propyl alcohol and total solids and on the solids content of the latex-base adhesive, and can be determined by the above formulae.

Compositions containing from 23 to '31 per cent by weight of total solids (18.5 to 25 per cent by weight of rubber solids) and from about 2 to 13 per cent by weight of propyl alcohol have been found satisfactory. The results are shown graphically in Fig. 2, which correlates the relationship between viscosity and propyl alcohol content for compositions having varying amounts of total solids, each point representing'one of my compositions. It will be seen that the viscosity of these compositions is increased by the presence of propyl alcohol, even in amounts as low as two per cent. All of the compositions have good penetrating and softening action, and are physically stable.

In order to provide an adhesive that can be allowed to dry prior to the edge folding operation any of the various permanent-type softening agents may be incorporated therein. The penetrating action ofmy adhesive carries the permanent softening agent well into the leather and deposits it there upon drying, an advantage over adhesives which may contain such softening agents but which are not so penetrating. Small amounts of permanent-type softening agents are adequate since good penetration is assured; although, if desired, as much as three per cent by weight of triethanol amine as a softening agent may be employed. Generally less than one per cent by weight of softening agent is sufiicient.

I prefer to incorporate the permanent-type softening agent with the propyl alcohol-water diluent and thereby, admixed with the diluent,

add it to the latex-base material. Frequently the softening agent, such as castor oil and sulfonated castor oil, is not miscible with the diluent, in which case an emulsion of diluent and softening agent can be prepared by any of several well known means.

Example 3 Mix three parts by weight of iso-propyl alcohol with 30 parts by weight of water. Then beat this mixture in a high speed mixer, for instance a Waring blender, add one part by weight of sulfonated castor oil and continue the beating until a stable emulsion forms. Then add this emulsion slowly while stirring to 100 parts by weight of BB Tex 818H cement. The resulting composition contains 27 per cent by weight total solids, 2.3 per cent by weight of iso-propyl alcohol and 0.8 per cent by weight of sulfonated castor oil. It is Well adapted for use in leather edge folding operations, being penetrating in action, thereby softening the leather and carrying the permanent softening agent well into the leather and it is stable physically. It can be allowed to dry and the leather will remain sufficiently soft to be folded. By employing the novel adhesive of my invention objectionable cracking is obviated in upper leather heretofore used, and in many cases the manufacturer is enabled to save substantial V amounts by employing leather of grades heretofore not considered suitable for edge folding.

Having thus disclosed my invention and described in detail illustrative examples thereof, I claim as new and desire to secure by Letters Patent:

1. A leather softening adhesive material comprising natural latex, propyl alcohol, and sulfonated castor oil having from 18 to 30 per cent by weight of natural rubber solids, from 2 to 18 per cent by weight of propyl alcohol and about 0.8 per cent by weight of sulfonated castor oil.

2. A leather softening adhesive highly penetrating to leather consisting essentially of natural latex, propyl alcohol and a permanent type leather softening agent such as castor oil and containing from 23 to 31 per cent total solids of which at least 80 per cent are natural rubber solids, from 2 to 18 per cent by weight of propyl alcohol and less than 3 per cent by weight of a leather softening agent of the permanent type.

3. The leather softening adhesive defined in claim 2 wherein the propyl alcohol is iso-propyl alcohol.

4. A leather softening adhesive highly penetrating to leather consisting essentially of natural latex, propyl alcohol and a permanent type leather softening agent such as castor oil, wherein natural rubber solids constitute at least 80 per cent of the total solids present, and containing from 2 to 18 per cent of propyl alcohol.

THURIBE GELINAS.

' REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,124,928 Lund Jan. 12, 1915 1,561,229 Haon Nov. 10, 1925 1,730,518 McGavach Oct. 8, 1929 2,001,791 Linscott May 21, 1935 2,117,258 Schidrowitz May 10, 1938 2,127,298 Isaacs Aug. 16, 1938 

1. A LEATHER SOFTENING ADHESIVE MATERIAL COMPRISING NATURAL LATEX, PROPYL ALCOHOL, AND SULFONATED CASTOR OIL HAVING FROM 18 TO 30 PER CENT BY WEIGHT OF NATURAL RUBBER SOLIDS, FROM 2 TO 18 PER CENT BY WEIGHT OF PROPYL ALCOHOL AND ABOUT 0.8 PER CENT BY WEIGHT OF SULFONATED CASTOR OIL. 